As disclosed in patent literature 1, for example, a flow of air generated during vehicle running rotates a motor to drive a vehicular cooling fan at a revolution speed higher than or equal to a predetermined value. In this case, a control device for the vehicular cooling fan switches MOSFET at a predetermined frequency to regenerate the energy generated by the motor when the MOSFET is provided for a lower arm of an inverter.
The control device for the vehicular cooling fan receives no directive to drive the cooling fan from an engine control device. The control device provides regeneration control when the motor revolution speed is higher than or equal to a predetermined value under the condition that a battery is not fully charged. The predetermined value to determine the motor revolution speed is configured to be a revolution speed capable of regenerating more energy than at least the energy used for the regeneration control to effectively improve an electric power balance. The control device according to patent literature 1 includes a position sensor to detect a magnetic pole position of a motor rotor in order to determine whether the regeneration control is feasible based on the motor revolution speed.
However, provision of the position sensor increases the number of parts and costs. The position sensor is used with difficulty and is less durable under poor conditions.
A publicly known technology can detect a magnetic pole position of the motor rotor without using sensors based on an induced electromotive force of an idle coil when the motor is driven. For this reason, the position sensor may be eliminated from the apparatus according to patent literature 1.
However, the following issue may arise if the position sensor is eliminated. A flow of air generated during vehicle running rotates the cooling fan and also the motor while the motor stops. If the control device for the cooling fan does not include the position sensor, the control device for the cooling fan cannot determine a magnetic pole position of the motor rotor when receiving a drive directive. To drive the motor, the control device for the cooling fan needs to first energize a specified energization phase, perform positioning control to position the rotor to a predetermined angle position, and then perform forced commutation to sequentially changes energization patterns.
As a result, eliminating the position sensor necessitates a long time to allow the motor to transition from a non-driving state to a driving state. In contrast, the control device for the cooling fan needs to start driving the cooling fan as soon as possible to cool objects to be cooled such as a radiator when receiving a drive directive from a higher-order engine control device.